The Internet of Things (IoT) is the network of physical objects or things embedded with electronics, software, sensors, and network connectivity, which enables these objects to collect and exchange data. The Internet of Things allows objects to be sensed and controlled remotely across existing network infrastructure, creating opportunities for more direct integration between the physical world and computer-based systems, and resulting in improved efficiency, accuracy and economic benefit. IoT devices include wearables such as smart watches, and sports sensors, as well as distributed sensors and actuators and enable technologies such as smart buildings or smart grids and the like.
A question arises as to how to communicate with IoT devices. In one possibility, narrowband FDM transmission may be used between IoT devices and a base station or eNodeB or Access Point or hot spot (collectively referred to as BS herein below), and in that case there may be a restriction on the number of frequency sub-bands or overall bandwidth that can be assigned to any individual device.
Peak-to-Average Power Ratio (PAPR) of the transmitted signals is a crucial factor in power-efficient communications and specifically for narrowband (NB) IoT as such. A large PAPR entails substantial limitations on the transmission power regime mainly due to non-linearity of the power amplifier (PA). A PA backoff is dictated according to the achieved PAPR, thus calling for a reduced average transmit power and evidently reducing the coverage range. The superior behavior of Single-Carrier FDM (SC-FDM) over OFDM in terms of PAPR was the main incentive for it being chosen as the modulation technique for the uplink of the E-UTRA standard (a.k.a. LTE).
However, the currently considered alternatives for NB-IoT transmission as part of the LTE specification has only narrow frequency allocation, and subsequently limited throughput, of only up to a few (e.g. 1, 2, 4 or 8) subcarriers (SCs) due to PAPR limitations. While transmission of SC-FDM over 1 or 2 SCs implies near 0 dB PAPR, the PAPR with, say, 32 SCs is around 8dB, which incurs a too high PA backoff and thus reduced coverage for these purposes.